The magnetoresistive materials used in a magnetoresistive sensing device would change its resistance due to the presence of magnetic field and they are widely applied in various industries such as sport products, vehicles, motors, communication devices, etc. Commonly used magnetoresistive materials can be classified into three categories: anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR), based on how they work and how sensitive they are.
In general, the magnetic field change to be measured by the magnetoresistive sensing device is very small and it can not be measured accurately without proper testing, setting and calibration done to the magnetoresistive sensing device. However, the trend of continuing miniaturization of device and complexity of package would make testing, setting and calibration more difficult, so a built-in self test unit is required to solve this problem.